Method of manufacturing a transmission belt

ABSTRACT

A method of manufacturing a ribbed vulcanized transmission belt having an elastomer cushion layer and an elastomer compression layer in which reinforcing fibers are embedded, wherein the method comprises forming a blank having at least a cushion layer and a compression layer, molding the blank under pressure in a mold provided with an imprint of a plurality of ribs, vulcanizing the blank, and machining off surplus material to uncover protruding ends of the reinforcing fibers in at least one region of each rib. In the vicinity of the surfaces of the ribs, the mean direction of the reinforcing fibers is substantially tangential to the surfaces of the ribs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of application Ser. No.08/915,043 filed Aug. 20, 1997, now U.S. Pat. No. 5,904,630.

The present invention relates to a method of manufacturing a vulcanizedtransmission belt referred to as a "ribbed" belt, in particular for anautomobile transmission, and to a belt obtained by implementing themethod.

BACKGROUND OF THE INVENTION

It is already known, in particular from European Patent ApplicationEP-642 886 (Mitsuboshi), that a ribbed belt can have a backing layer, acushion layer in which cords are disposed longitudinally, and a"compression" layer in which reinforcing fibers are embedded in alateral direction of the belt, and on which the ribs of the belt areformed by machining a plane blank, generally by means of a grindingroller, which wastes a considerable amount of material, namely about30%. Such machining of the ribs uncovers the ends of the reinforcingfibers so that they protrude from the outside of the ribs, and it alsonicks the surface of the ribs, thereby forming tear start lines, inparticular in the convex regions where the top of each rib meets itssides.

European Patent Application EP-633 408 proposes to apply a thin layer ofrubber to the top of each of the ribs so as to coat the protrudingfibers and to eliminate the tear start lines. This complicatesmanufacturing by adding another step.

The solution proposed in Application EP-642 886, which consists in notmachining the tops of the ribs and in creating a concave recessed zonebetween the flat top of each rib and each of its sides, the recessedzone not making contact with the pulley, makes it possible to solve theproblem only where it is at its worst, without remedying the problem ofthe tear start lines that machining can cause, or the problem of wastageof material.

In practice, the life of machined belts is generally shorter than thatof other types of belt.

It is however desirable to have belts whose ribs have protruding fibersbecause such fibers tend to reduce the operating noise of the belt incertain applications.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to provide a method of manufacturing aribbed transmission belt whose ribs have protruding fibers and which hasa long life.

Another object of the invention is to provide a method of manufacturinga belt, which method minimizes wastage of material.

The invention thus provides a method of manufacturing a ribbedvulcanized transmission belt having an elastomer cushion layer in whichlongitudinally disposed cords are embedded, and an elastomer compressionlayer in which reinforcing fibers are embedded and on whichlongitudinally extending ribs are provided, at least a region of thesurface of each of the ribs having protruding fibers protruding from it,said method comprising the following steps:

a) forming a blank having at least said cushion layer and saidcompression layer;

b) molding said blank under pressure in a mold provided with an imprintof the ribs, said imprint having an outline such that each of the ribson the belt has surplus material of nominal thickness e in said region;

c) vulcanizing said blank;

d) machining the ribs on the belt to their final dimensions by removingsaid surplus material so as to uncover protruding ends of the fibers.

The nominal thickness e preferably lies substantially in the range onceto twice the thickness of the layer of skin of elastomer at the surfaceof the ribs and preferably in the range once to 1.5 times saidthickness.

For example, the nominal thickness e may lie in the range 0.1 mm to 0.3mm.

In the method the length of the fibers may lie in the range 0.5 mm to 10mm, and the proportion by weight of the fibers in the compression layermay lie in the range 2 parts to 30 parts for 100 parts of elastomer.

Said region having protruding fibers may be the side of each of theribs. In a variant, the entire surface of each of the ribs hasprotruding fibers.

The invention also provides a ribbed transmission belt having anelastomer cushion layer in which longitudinally disposed cords areembedded, and an elastomer compression layer in which reinforcing fibersare embedded and on which longitudinally extending ribs are provided,said fibers protruding from at least a region of the surface of each ofthe ribs, wherein, at least in said region and in the vicinity of thesurfaces of the ribs, the mean direction of the reinforcing fibers issubstantially tangential to the surfaces of the ribs.

In cross-section, the ribs advantageously have lines of movement of thefolds of the elastomer that follow the outline of the ribs during amolding operation, and the mean direction of the fibers follows saidlines of movement.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention appear moreclearly on reading the following description given by way ofnon-limiting example and with reference to the accompanying drawings, inwhich:

FIG. 1 is a cross-section view through a belt machined using a prior artmethod;

FIGS. 2a and 2b are cross-section views through a belt molded andmachined using the method of the invention, the views being respectivelybefore and after machining; and

FIG. 2 is an enlarged, detailed view of a section of FIG. 2a;

FIGS. 3a to 3c show the method of the invention.

MORE DETAILED DESCRIPTION

The machined belt shown in FIG. 1 comprises a backing layer 11, in whicha woven reinforcement is optionally embedded, a cushion layer 12 ofelastomer material in which cords 14 are embedded, the cords being madeof, for example, polyester, polyamide, or aramid fibers, and acompression layer 15 in which reinforcing fibers 17 are embedded.

Manufacturing such a belt involves making up a plane blank formed of astack of layers, and vulcanizing said blank in an autoclave at apressure approximately in the range 6 bars to 8 bars.

After vulcanization, the ribs 16 are machined by grinding to produce thebelt shown in FIG. 1, in which protruding fibers 18 protrude from thesides 19 of the ribs 16. As shown in FIG. 1, the general direction ofthe fibers 17 is the transverse direction (i.e. parallel to thecross-section plane), and parallel to the faces 2 and 3 of the belt.After machining, the protruding fibers 18 naturally remain in thegeneral direction of the fibers 17.

In addition to involving considerable wastage of material (about 30%),such machining by removing material also weakens to a certain extent themachined surfaces of the ribs 16, i.e. the sides 19 of the ribs in thisexample, as shown by above-mentioned European Patent Application EP-633408.

The belt of the invention, shown in FIG. 2a after it has been molded andvulcanized, and in FIG. 2b after it has been machined, comprises abacking layer 21 having external surface 32, in which a wovenreinforcement is optionally embedded in the backing layer 21, a cushionlayer 22 in which cords 14 are embedded, the cords being made of, forexample, polyester, polyamide, or aramid fibers, etc., and a compressionlayer 25 in which fibers 27 are embedded, the fibers being, for example,natural or synthetic fibers of length in the range 0.5 mm to 10 mm, andpresent in the compression layer 25 in a proportion by weight in therange 2 parts to 30 parts for 100 parts of elastomer, for example.

Manufacturing a belt of the invention involves making up a plane blankformed of a stack of layers, molding said blank, e.g. in a hydraulicmold at a pressure of 20 bars, and then vulcanizing it so as to obtainthe belt shown in FIG. 2a. This belt is provided with ribs 26 whoseoutline is molded, each of the ribs 26 having a top 33 and sides 31, butthis outline not being molded to the final dimensions of the ribs 26.The subsequent machining step gives the final belt shown in FIG. 2b.

As shown in FIG. 2a, the general direction of the fibers 27 is verydifferent from that of the fibers shown in FIG. 1. During molding, thefibers 27 tend to be aligned with the lines of movement of the folds ofthe rubber, which lines follow the outline of the ribs 26. The closerthe lines of movement are to the surfaces of the ribs 26 the morefaithfully they follow said outline of the ribs. In the vicinity of thesurfaces of the ribs, the general direction of the fibers 27 is almostparallel to the surface of each rib 26 on the sides 31 and on the top33. In the regions 35 where the top meets the sides 31, and in thegrooves 36 between the ribs 26, the general direction changesprogressively. Furthermore, it can be observed that, after molding, alayer of skin or limit layer 34 of thickness d exists at the surface(31, 33) of each of the ribs 26, in which layer the fibers 27 are notpresent (see detail in FIG. 2). This layer has a depth of about 0.1 mm.

The machining step of the invention consists in removing the layer ofskin 34, and in setting the machining depth preferably so that it isjust enough to uncover the ends 28 of the fibers 27 bordering on thelayer of skin 34. Such machining to a depth that is only slightlygreater than the depth of the layer 34, prevents nicks from being formedin the surface of the elastomer of the ribs 26, and thereby preventstear start lines from forming in said surface, which would reduce thelife of the belt. Furthermore, although, in the vicinity of the wall 31,the preferred direction of the fibers 27 is substantially parallel tosaid wall, it can be observed that there is a significant dispersion inthe directions of the fibers 27, which dispersion is much greater thanthat of the fibers 17 in FIG. 1. This dispersion improves the cushioneffect procured by the fibers 27, in particular on the sides 31 of theribs.

COMPARATIVE EXAMPLE

This example corresponds to an accelerated ageing test implemented byequipping a Diesel engine successively with three belts of the same type(6 ribs having a pitch of 3.56 mm), but manufactured using differentmethods, namely:

belt No. 1: a belt machined using a prior art method;

belt No. 2: a belt molded using a prior art method; and

belt No 3: a belt molded and machined using a method of the invention.

The test was continued until the layers 12 and 15 (or 22 and 25) wereobserved to separate.

For a life equal to 100 for belt No. 1, a life equal to 142 was observedfor belt No. 2, and a life equal to 173 was observed for belt No. 3.

The machined belt had the shortest life. It should be noted that thetest implemented was a delamination test for which the vulcanizationpressure or the molding pressure was very significant.

Comparing the lives of belt No. 3 and of belt No. 2, which belts weremolded at the same pressure, shows that the additional machining step ofthe invention significantly increases the life of the belt, which isparticularly surprising in view of the teaching of above-mentionedEuropean Patent Application EP-633 408. In addition, the life of beltNo. 3 is much longer than that of belt No. 1, even though the method ofmanufacturing it is much more economical because the machining step ofthe invention involves removing a marginal thickness of materialresulting in removing a few percent of the material (as compared withthe removal of about 30% of the material in a machined belt).

FIGS. 3a to 3c show the method of the invention.

FIG. 3a shows how a blank is made comprising the layers 21, 22, and 25.The general direction of the fibers 27 is transverse (i.e. parallel tothe cross-section plane), and parallel to face 2.

FIG. 3b shows how the blank is molded under pressure in a hydraulic mold50 having an imprint 51 whose outline corresponds to that of the ribs 26prior to machining (FIG. 2a). The vulcanization step is generallyperformed in the hydraulic mold 50, at a pressure of about 20 bars.

FIG. 3c shows how the machining step is performed using a grindingroller 60 having the imprint 61 of the ribs 26 in their finaldimensions. For this purpose, the vulcanized blank is mounted to rotateon pulleys 62 and 63, and the grinding roller 60 is brought towards theblank to rectify it to the desired depth, as indicated above, to obtainthe belt shown in FIG. 2b. After machining, the belt is generally cut upin known manner into a plurality of individual belts.

I claim:
 1. A method of manufacturing a ribbed vulcanized transmissionbelt having an elastomer cushion layer in which longitudinally disposedcords are embedded, and an elastomer compression layer in whichreinforcing fibers are embedded and on which longitudinally extendingribs having defined sides are provided, at least a region of the surfaceof each of the ribs having protruding fibers protruding from each saidrib, said method comprising the following steps:a) forming a blankhaving at least said cushion layer and said compression layer; b)molding said blank under pressure in a mold provided with an imprint ofthe ribs, said imprint having an outline such that each of the ribs onthe belt has surplus material in said region forming a skin of elastomerat the surface of the ribs, the surplus material being of nominalthickness e at least equal to the thickness of the skin of elastomer atthe surface of each of the ribs; c) vulcanizing said blank; d) machiningthe ribs on the belt to desired final dimensions by removing saidsurplus material of thickness e so as to uncover protruding ends of saidfibers bordering said skin, the thickness e being chosen such that theprotruding end of said fibers bordering said skin appear on performingsaid machining.
 2. A method according to claim 1, wherein said nominalthickness e lies substantially in the range once to twice the thicknessof the layer of skin of elastomer at the surface of the ribs.
 3. Amethod according to claim 2, wherein said nominal thickness liessubstantially in the range 0.1 mm to 0.3 mm.
 4. A method according toclaim 1, wherein the fibers are of length lying in the range 0.5 mm to10 mm, and are present in the compression layer in a proportion byweight lying in the range 2 parts to 30 parts for 100 parts ofelastomer.
 5. A method according to claim 1, wherein the step d) isperformed with a rotary grinding roller having an outline correspondingto an inverse configuration of said final dimensions of said ribs to beobtained by machining.
 6. A method according to claim 1, wherein saidregion is the side of each of the ribs.
 7. A method according to claim1, wherein said region is the entire surface of each of the ribs.